1. Field of the Invention
The present invention relates to a display apparatus and a control method thereof.
2. Description of the Related Art
Conventionally, as a technology related to a liquid crystal display apparatus, a technique of using a backlight including a plurality of light sources, and controlling the emission brightness of each light source and the transmittance of the liquid crystal panel according to the brightness of the image to be displayed has been proposed (Japanese Patent Application Laid-open No. 2002-99250). Specifically, with the technology described in Japanese Patent Application Laid-open No. 2002-99250, the emission is controlled so that the emission brightness becomes lower in a dark region of the image in comparison to a bright region. Based on this kind of control, it is possible to reduce a misadjusted black level, and improve the contrast of the displayed image (image displayed on the screen).
With the conventional technology described above, when superimposing a graphic image on an original image and displaying the same, as with an on-screen display (OSD), for example, the emission brightness of each light source is controlled according to the brightness of the composite image that is obtained by compositing the graphic image with the original image. Nevertheless, when this kind of control is performed, in cases where the brightness of the graphic image differs considerably from the brightness of the original image (surrounding image) in a region surrounding the graphic image in the composite image, the picture quality of the original image (specifically, the surrounding image) will deteriorate considerably in the displayed image. For example, when the graphic image is extremely dark in comparison to the surrounding image in the composite image, a misadjusted black level of the surrounding image will arise in the displayed image.
Note that, when a graphic image is superimposed on an original image and is displayed, controlling the emission brightness of each light source according to the brightness of the original image may also be considered. When this kind of control is performed, the original image can be displayed without deteriorating the picture quality. Nevertheless, in cases where the brightness of the graphic image differs considerably from the brightness of the surrounding image in the composite image, the picture quality of the graphic image will deteriorate considerably in the displayed image. For example, when the surrounding image is extremely dark in comparison to the graphic image in the composite image, the visibility of the graphic image in the displayed image will deteriorate.
Conventional technology that gives consideration to the foregoing problems is disclosed, for example, in Japanese Patent Application Laid-open No. 2011-209407. With the technology disclosed in Japanese Patent Application Laid-open No. 2011-209407, the target brightness of each light source is decided according to the brightness of the original image, and the target brightness is corrected according to the brightness of the composite image.
There are various types of graphic images. For example, as graphic images, there is a graphic image of a type (first type) in which the picture quality of the original image should be preferentially controlled in comparison to the picture quality of the graphic image. Moreover, as graphic images, there is a graphic image of a type (second type) in which the picture quality of the graphic image should be preferentially controlled in comparison to the picture quality of the original image. Nevertheless, with the technology disclosed in Japanese Patent Application Laid-open No. 2011-209407, the emission brightness is controlled so that the deterioration in the picture quality of both the graphic image and the original image is suppressed. Thus, while it is possible to suppress the deterioration in the picture quality of the graphic image to a certain extent and suppress the deterioration in the picture quality of the original image to a certain extent, when the graphic image is the graphic image of the foregoing first type or second type, the emission brightness cannot be appropriately controlled. For example, when the graphic image is the foregoing first type graphic image, since the target brightness is corrected so as to suppress the deterioration in the picture quality of the graphic image, it is not possible to control the emission brightness so that the deterioration in the picture quality of the original image is sufficiently suppressed. Moreover, when the graphic image is the foregoing second type graphic image, since the target brightness is corrected only to a level of maintaining the picture quality of the original image, it is not possible to control the emission brightness so that the picture quality of the graphic image is sufficiently suppressed.